This invention relates to a touch response device for an electronic musical instrument and, more particularly, to a touch response device of an improved touch control system for controlling tone color, tone pitch, tone volume etc. of a tone in response to an operation touch during performance of operation means such as keys in a keyboard instrument.
There are an initial touch control which controls tone color, tone pitch, tone volume etc. of a tone in response to key depression speed and an after touch control which controls tone color etc. of a tone by detecting a key depression force during sustaining of key depression. As a prior art of this touch response control, there are techniques disclosed in Japanese Patent Publication No. 61-14518 corresponding to U.S. Pat. No. 4,301,704 and Japanese Preliminary Patent Publication No. 1-200289 corresponding to U.S. Pat. No. 4,979,423. U.S. Pat. No. 4,301,704 discloses a touch response control which is made in accordance with initial touch data which is formed by detecting a difference between operation times of two contacts produced in accordance with key depression speed and after touch data which is formed in response to a detection signal from pressing force detection devices consisting of a piezoelectric element and provided for respective keys of a keyboard. U.S. Pat. No. 4,979,423 discloses a touch response control according to which pressing force detection devices producing first and second detection signals of mutually different output response characteristics depending upon key depression force are provided for respective keys of a keyboard and the first detection signal is used as an initial touch signal and the second detection signal is used as an after touch signal. As other prior art concerning the touch response control, there are techniques disclosed in Japanese Preliminary Patent Pubication No. 59-105692 and Japanese Patent Publication No. 52-46088 corresponding to U.S. Pat. No. 3,882,751.
Japanese Patent Publication No. 63-42268 corresponding to U.S. Pat. No. 4,528,885 discloses a control according to which, in order to enable a touch response control to be made from a time point immediately after depression of a key even when rising of an after touch detection signal has been delayed, there is formed a tone control signal which gradually changes toward an initial touch signal which is a target value during a predetermined period of time from start of depression of a key and changes thereafter following an after touch signal, and a tone is controlled in accordance with this tone control signal. In this control, for enabling the tone control signal which has once reached a target value corresponding to an initial touch signal to follow an after touch signal thereafter, one of two following coefficients is selectively used depending upon whether the current value of the tone control signal is larger or smaller than the current value of the after touch signal. More specifically, when the current value of the tone control signal is larger than the current value of the after touch signal, a first following coefficient having a negative inclination is used, whereas when the current value of the tone control signal is smaller than the current value of the after touch signal, a second following coefficient having a positive inclination is used. Accordingly, when the current value of the tone control signal is larger than the current value of the after touch signal, the tone control signal changes with a certain negative inclination corresponding to the first following coefficient and, thereafter, as the current value of the tone control signal becomes smaller than the current value of the after touch signal, the tone control signal changes with a certain positive inclination corresponding to the second following coefficient.
In all of the after touch control techniques described in the above prior art publications, a state in which a pressing force against the pressing force detection devices is zero (i.e., a state in which no after touch signal is produced) is used as a reference, and tone volume, tone pitch, tone color, tonal effects etc. are increased or decreased in a positive direction (a direction in which the output value is larger than a normal output value produced in a case where the after touch control is not made) or in a negative direction (a direction in which the output value is smaller than a normal output value produced in a case where the after touch control is not made) with respect to the output value of the after touch signal in accordance with the magnitude of an absolute output value of the after touch signal. Thus, the prior art after touch control is made in only one of the positive and negative directions from the normal output value of tone volume, tone pitch, tone color, tonal effect etc. of a tone which is used as a borderline.
In natural musical instruments such as violin, tone volume and tone pitch after sounding of a tone can be increased or decreased in either positive or negative direction as desired by the player. In the above described prior art electronic musical instruments, however, the touch control can be made only in one direction, so that it is not possible to increase or decrease tone volume, tone pitch etc. as freely as in natural musical instruments and performance expression by the electronic musical instruments therefore is inferior to that of natural musical instruments.